Human immunodeficiency virus (HIV) infection is the determining factor in the development of acquired immunodeficiency syndrome (AIDS). At present there is no effective vaccine against this disease. The objectives of this project are to characterize HIV antigens, determine the targets of humoral and cell mediated immunity, and to use this information to develop candidate vaccines. We have constructed recombinant vaccinia viruses containing genetic information of HIV and the closely related simian immunodeficiency virus. These recombinant viruses have been used to prepare purified immunogens, monoclonal antibodies, targets for cytotoxic T cells and candidate vaccines. During the past year, we used a panel of monoclonal antibodies to identify and map conserved epitopes in the gp41 portion of the HIV-1 envelope glycoprotein. In addition, we constructed a chimeric gene encoding the cytoplasmic and transmembrane domains of a vaccinia virus envelope protein attached to the extracellular domain of the HIV-1 envelope protein. This novel glycoprotein was displayed on the surface of vaccinia virus particles and induced an enhanced immune response in small animals.